In fermented malt beverages such as beer and the like with malt as a raw material, chemical reactions such as oxidation and the like are accelerated due to the passage of time, the rise in temperature, and so on, thereby deterioration of the products is progressed. Products once deteriorated suffer damage to their original taste and flavor contained in fermented malt beverages and their quality is deteriorated. In order to prevent such quality deterioration in fermented malt beverages, various attempts have been made as shown below.
The publication of Japanese Laid-Open Patent Application No.1993-137555 describes a process referring to the use of malt wherein lipid is removed in advance from the beer malt by sub-critical or super-critical carbon dioxide, as a process for producing beer with the use of malt from which lipid, which damages quality, has been selectively and efficiently removed without affecting enzymes in the malt, in beer or in the beer production steps. According to the description, the filtering efficiency, foam-lastingness and flavor stability will improve, yet this process requires a step of treating raw materials with super-critical carbon dioxide, which leads to the increase in the production cost.
The publication of Japanese Laid-Open Patent Application No.2000-4867 describes as a production process for malt alcoholic beverages with high flavor lastingness and a management method for controlling the generation of a substance which indicates the flavor lastingness in an intermediate sample in the production process for malt alcoholic beverages including the steps of: selection of raw materials including malt; wort production; fermentation; maturation; filtration; and container filling. The description continues that 5-hydroxymethylfurfural (5-HMF) or its precursor is selected as an indicator for flavor lastingness and malt alcoholic beverages with high flavor lastingness can be produced by successfully suppressing this indicator substance in the course of production. It further discloses specific examples including a method of suppressing 5-HMF generation by adding an amino acid which has a thiol group and a method of giving the anti-oxidation property to the wort by the addition of catechin. But in order to raise the effectiveness of suppressing 5-HMF generation, multiple execution of the treatment process will be required and the steps are anticipated to become complicated.
The following mechanisms have been presented with regard to the generation of a beer stale flavor which deteriorates the taste of fermented malt beverages such as beer and the like. They are: Maillard reaction and Strecker degradation of amino acids; autoxidation of fatty acids and enzymatic oxidation of lipids; oxidative degradation of a bitter substance in the hop, oxidation of higher alcohols by melanoidines, oxidation of the unsaturated hydroxyfatty acid or alcohols catalyzed with a metal ion (Cu, in particular); and oxidation of a higher alcohol. These or some among these are thought to be involved in the generation of a stale flavor (Hideo MIYAJI, “Beer Brewing Technology”, Shokuhin Sangyo Shimbunsha, Co., Ltd., published on Dec. 28, 1998; pp. 418–424).
On the other hand, a stale flavor itself has been studied. Trans-2-nonenal is exemplified as one of the substances causing a stale flavor. One of the generation pathways for this substance is as follows: a trans-2-nonenal precursor (a hydroxide derivative), derived from lipid or the fatty acid in the raw material, is generated upon both enzymatic and non-enzymatic oxidations in the course of wort preparation, which further leads to the generation of trans-2-nonenal through the oxidative degradation. It is argued that, even though the above-mentioned precursor is removed to a high degree in the courses of fermentation and maturation, the precursor transfers on to the finished beer and then, by the later oxidation, trans-2-nonenal generates in the beer and the like. It is, however, rather thought that trans-2-nonenal produced in the wort forms Schiff bases with primary amines, such as amino acids, in the wort and that some of the Schiff bases are passed on to the beer and the like, where trans-2-nonenal is freed from Schiff bases depending on the temperature- or pH-condition, although many of them are removed in the courses of fermentation and maturation (Lermusieau et al., J. Am. Soc. Brew. Chem. 57, 1999, p29–33).
The subject of the present invention is to provide a process for producing wort with reduced content of a stale flavor-causing substance for the purpose of producing fermented malt beverages such as beer and the like in which a stale flavor generation is suppressed, and to provide fermented malt beverages such as beer and the like in which a stale flavor generation is suppressed, that are produced by using wort with low content of a stale flavor-causing substance obtained by this production process.
In the course of studying the suppression of the generation of a stale flavor in beer, the present inventor focused on trans-2-nonenal among various substances causing a stale flavor and analyzed in details the behavior of a trans-2-nonenal precursor in the beer production steps. The present inventor then found out that in order to estimate the levels of trans-2-nonenal in the beer products generated during storage, it is important to grasp prosperity and decay of a trans-2-nonenal precursor in the wort, and that the trans-2-nonenal level, in the wort adjusted to a certain pH and boiled for a certain time, namely trans-2-nonenal potential (hereinafter NP), serves as an effective indicator for a stale flavor generated in the beer products. In addition, the present inventor found out that sugar content in the sparged wort decreases gradually since the last extract is washed out of the spent grains, whereas NP content holds a high level without correlating to the decrease in sugar content during sparging. The present invention has come to the completion based on these findings.